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Avalanche Forecast

Archived

Apr 15th, 2013–Apr 16th, 2013

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

This bulletin was produced using limited data streams, and significant variations in snowpack structure are likely to exist. If you've been traveling in the backcountry, we'd love to hear from you. Observations can be sent to [email protected].

Confidence

Poor - Due to variable snowpack conditions

Weather Forecast

Tuesday: No snow. Moderate E winds. Freezing level near 1200 m, dropping to 200 m overnight.Wednesday: Light snow. Light W winds. Freezing level near 1500 m, dropping to 1100 m overnight.Thursday: Light snow. Light W winds. Freezing level near 1700 m, dropping to 1100 m overnight.

Avalanche Summary

On Sunday, a naturally triggered size 2.5 slab failed on a buried crust. Numerous small loose dry avalanches were also observed. In neighbouring Glacier National Park, skiers triggered a size 3 slab on a buried crust on an east aspect in the alpine on Monday. The slab above this interface may be reaching tipping point with incremental loading from snow and wind.

Snowpack Summary

Around 40 cm recent storm snow has been shifted by variable winds into wind slabs at treeline and above. In some areas, a trace of new snow overlies a refrozen surface on southerly aspects and below 2000 m on northerly aspects. A weak interface in the upper metre of the snowpack consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. Recent activity in Glacier National Park and the North Columbia regions demonstrates that this interface has the potential for surprisingly large avalanches. Cornices in the region are potentially destructive. Periods of warming or solar radiation may increase the reactivity of cornices and storm slabs.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.